Implementation of true asynchronous signaling between processes

Communication between Erlang processes has conceptually always been
performed through asynchronous signaling. The runtime system
implementation has however previously preformed most operation
synchronously. In a system with only one true thread of execution, this
is not problematic (often the opposite). In a system with multiple threads
of execution (as current runtime system implementation with SMP support)
it becomes problematic. This since it often involves locking of structures
when updating them which in turn cause resource contention. Utilizing
true asynchronous communication often avoids these resource contention
issues.

The case that triggered this change was contention on the link lock due
to frequent updates of the monitor trees during communication with a
frequently used server. The signal order delivery guarantees of the
language makes it hard to change the implementation of only some signals
to use true asynchronous signaling. Therefore the implementations
of (almost) all signals have been changed.

Currently the following signals have been implemented as true
asynchronous signals:
- Message signals
- Exit signals
- Monitor signals
- Demonitor signals
- Monitor triggered signals (DOWN, CHANGE, etc)
- Link signals
- Unlink signals
- Group leader signals

All of the above already defined as asynchronous signals in the
language. The implementation of messages signals was quite
asynchronous to begin with, but had quite strict delivery constraints
due to the ordering guarantees of signals between a pair of processes.

The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts
that service all kinds of signals. More details regarding the signal
queue can be found in comments in the erl_proc_sig_queue.h file.

The monitor and link implementations have also been completely replaced
in order to fit the new asynchronous signaling implementation as good
as possible. More details regarding the new monitor and link
implementations can be found in the erl_monitor_link.h file.

1 files changed, 17 insertions, 23 deletions

diff --git a/erts/emulator/beam/erl_hl_timer.c b/erts/emulator/beam/erl_hl_timer.c
index bda2c9b94d..6ec6f8065e 100644
--- a/erts/emulator/beam/erl_hl_timer.c
+++ b/erts/emulator/beam/erl_hl_timer.c
@@ -1,7 +1,7 @@
 /*
  * %CopyrightBegin%
  * 
- * Copyright Ericsson AB 2015-2017. All Rights Reserved.
+ * Copyright Ericsson AB 2015-2018. All Rights Reserved.
  * 
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -38,6 +38,7 @@
 #define ERTS_WANT_TIMER_WHEEL_API
 #include "erl_time.h"
 #include "erl_hl_timer.h"
+#include "erl_proc_sig_queue.h"
 #ifdef ERTS_MAGIC_REF_BIF_TIMERS
 #include "erl_binary.h"
 #endif
@@ -2470,28 +2471,21 @@ access_bif_timer(Process *c_p, Eterm tref, int cancel, int async, int info)
 	    req->rrefn[1] = rrefn[1];
 	    req->rrefn[2] = rrefn[2];
 
-	    erts_proc_lock(c_p, ERTS_PROC_LOCKS_MSG_RECEIVE);
-
-	    if (ERTS_PROC_PENDING_EXIT(c_p))
-		ERTS_VBUMP_ALL_REDS(c_p);
-	    else {
-		/*
-		 * Caller needs to wait for a message containing
-		 * the ref that we just created. No such message
-		 * can exist in callers message queue at this time.
-		 * We therefore move the save pointer of the
-		 * callers message queue to the end of the queue.
-		 *
-		 * NOTE: It is of vital importance that the caller
-		 *       immediately do a receive unconditionaly
-		 *       waiting for the message with the reference;
-		 *       otherwise, next receive will *not* work
-		 *       as expected!
-		 */
-		ERTS_MSGQ_MV_INQ2PRIVQ(c_p);
-		c_p->msg.save = c_p->msg.last;
-	    }
-	    erts_proc_unlock(c_p, ERTS_PROC_LOCKS_MSG_RECEIVE);
+            /*
+             * Caller needs to wait for a message containing
+             * the ref that we just created. No such message
+             * can exist in callers message queue at this time.
+             * We therefore move the save pointer of the
+             * callers message queue to the end of the queue.
+             *
+             * NOTE: It is of vital importance that the caller
+             *       immediately do a receive unconditionaly
+             *       waiting for the message with the reference;
+             *       otherwise, next receive will *not* work
+             *       as expected!
+             */
+            ERTS_RECV_MARK_SAVE(c_p);
+            ERTS_RECV_MARK_SET(c_p);
 
 	    ERTS_BIF_PREP_TRAP1(ret, erts_await_result, c_p, rref);
 	}